1. Field of the Invention
The present invention relates to a unit for varying a temperature of a test piece by controlling a temperature of a control face. The present invention further relates to testing instruments incorporating the unit for environmental tests such as temperature and humidity chambers and for temperature tests of semiconductor wafers, electronic components and the like.
2. Description of Related Art
Temperature tests for electronic components such as integrated circuits are conventionally performed as burn-in tests. The burn-in tests of integrated circuits are done by separating several integrated circuits formed on a semiconductor wafer into individual bare dies and exposing each of the integrated circuits, which are packaged with sealing each separated bare die, in high temperature while turning electricity through the circuit. By means of the burn-in tests, it is enabled to reveal potential drawbacks in the integrated circuits within a short period of time and remove defects effectively by initial malfunction and aged deterioration.
Such burn-in tests, though, take a lot of time since they require individual packaged integrated circuits to be mounted at testing instruments. Further, the individual packaged integrated circuits have to be heated, resulting in troubles such as enlargement of testing instruments and increase of heat. Still further, the integrated circuit which is discriminated as a defect by the burn-in tests has to be disposed of, resulting in a factor to cause useless process of package.
Recently, the demand of a bare chip mounting is increased. The bare chip mounting is the method to separate a plurality of integrated circuits formed on a semiconductor wafer into individual bare dies and mount the separated bare dies directly at a board. In order to achieve such a bare chip mounting and excluding useless packaging, testing instruments of a burn-in test during a state of the semiconductor wafer is now being developed.
FIGS. 8A–8D show an example of a unit 101, for varying a temperature of a test piece, to be incorporated in a testing instrument in the related art. FIG. 8A is a front view of the unit 101, FIG. 8B is a bottom view thereof, FIG. 8C is a cross-sectional view taken along line C—C of FIG. 8A, and FIG. 8D is a cross-sectional view taken along line D—D of FIG. 8B.
The unit 101 comprises a disc-shaped hollow plate 102 provided with a heater 103 and a piping 102e. The heater 103 is a sheathed heater of an annular shape secured to a bottom face 102b of the plate 102. The plate 102 has a ring-shaped cavity 102e therein, which functions as a piping 102e. The piping 102e has one end being an opening 102c for supplying coolant and the other end being an opening 102d for recover the coolant. A temperature sensor 104 is attached on an outer peripheral wall of the plate 102.
FIG. 9 is an example of a schematic illustration of a testing instrument 100 using such a unit 101 in the related art. A temperature controller 130 controls to energize the heater 103 and also controls a cooling circuit 150 so that the unit 101 can be heated and cooled.
The cooling circuit 150, which is formed by connecting in series a compressor 151, a condenser 152, an expansion valve 153 and a primary side of a heat exchanger 141, is a cooling circuit for circulating the coolant consisting of refrigerant such as a hydrofluorocarbon or a hydrochloro-fluorocarbon therein. A secondary coolant circuit (viz. a brine circuit) 140, which is formed by connecting in series the unit 101, a circulating pump 142 and a secondary side of the heat exchanger 141, is a circuit for circulating a brine (viz. salt water) by the pump 142.
In the cooling circuit 150, the refrigerant compressed at the compressor 151 is liquefied by cooling at the condenser 152, and the liquefied refrigerant flows into the heat exchanger 141 in liquid phase or in gas-liquid mixture phase while being decompressed with the expansion valve 153. Then latent heat of vaporization of the refrigerant absorbs heat from the brine which flows in the secondary side of the heat exchanger 141. On the other hand, in the secondary coolant circuit 140, the brine cooled by the heat exchanger 141 flows into the unit 101, flowing in the piping 102e so as to cool the hollow plate 102. Then the brine with increased temperature flows out of the plate 102, returns through the circulating pump 142 to the heat exchanger 141 and circulates with being cooled again.
In other words, the temperature controller 130 controls the compressor 151 for adjusting the temperature of the brine to be cooled, so as to cool the unit 101 while adjusting the temperature of the brine which circulates in the unit 101.
The testing instrument 100 in the related art shown in FIG. 9 performs a semiconductor wafer burn-in test according to the following procedure. The heater 103 and the compressor 151 are controlled so that the temperature detected by the temperature sensor 104 corresponds to predetermined temperature at the temperature controller 130. On the other hand, a semiconductor wafer 120 (a test piece) to be brought to the burn-in test is put on a top face 102a (a control face) of the unit 101 and then a prober 110 is put on the semiconductor wafer 120 so as to cover the top face thereof. Thereby a number of probes 111 on the prober 110 come in contact with bumps 121 on the semiconductor wafer 120 so as to turn electricity through each integrated circuit of the semiconductor wafer 120 from a testing controller 131 via the prober 110.
In such arrangement, the semiconductor wafer 120 is driven in the energized condition determined at the testing controller 131, while the burn-in test is performed under temperature determined at the unit 101, so that an abnormal chip is detected at the testing controller 131 for being distinguished from a normal chip.
However, the testing instrument 100 in the related art shown in FIG. 9 employs a structure to flow the coolant toward one direction in the piping 102e for cooling the unit 101. In this case, it is required that the coolant should not cause a change of phase while flowing in the piping 102e. That is because the temperature of the top face 102a of the hollow plate 102 is not maintained uniformly and a cooling efficiency of the coolant decreases, both resulting from a remarkable change of a heat transfer rate, when the coolant causes a change of phase while flowing in the piping 102e. 
Consequently, the testing instrument 100 in the related art shown in FIG. 9 had to employ a structure to circulate the brine, which causes no change of phase regardless of fluctuation of an amount of heat, in the secondary coolant circuit 140 for cooling the unit 101, and to cool the brine circulating in the secondary coolant circuit 140 by use of another cooling circuit 150. In such a structure, a system for cooling the unit 101 is extremely complicated, resulting in preventing stability and response of temperature control and/or reduction of volume and cost of apparatus.
It is therefore an object of the present invention made in view of the problems and drawbacks described above to provide an advanced unit for varying a temperature of a test piece with a simple structure which has improved stability and response of temperature control. It is a further object of the present invention proposed simultaneously is to provide an advanced testing instrument employing the unit described above for achieving reduction of volume and cost thereof.